High Wattage Electrostatic Loudspeakers

[ak_47_boy]

Say you had a 100watt amplifier, 1kw amplifier, and a panel with a 100:1 step up transformer.
The final drive voltage would be 2800v for the 100watt amp and 9000v for the 1kw. The 1kw will obviously be able to play louder but will it actually be using 100mA @ 9000v?

I don't understand where 1kw of power goes. It's not heat or sound.

[SY]

Actually, heat and sound are exactly where it goes.

An ESL is a big capacitor. To get from zero to some voltage requires current. To get from zero to that voltage even faster takes more current. Now, when it's time to go back to zero, the higher the available current, the faster it can happen. But where does that current go? Yes, right back to the amplifier. Being reactive, to a first approximation the speaker absorbs no power, but the amp does. And that's where the heat goes; remember power factor, too.

Now, when we refine the approximation, we can see where the sound energy goes, but it's still a small proportion of the electrical energy that the amplifier needs to source and sink charging currents. It's an interesting exercise to calculate how much current it would take to drive a 1nF capacitor (a typical ESL value) at 20kHz.

[ak_47_boy]

Wow that actually works out to 8 ohms.

[Eva]

A class D amplifier would be a good alternative for driving a highly reactive load because all the reactive energy is returned back to the PSU. In case of a capacitive load (ESL), the amplifier may be designed so that the load forms part of the output LC filter (although the resonance that results when the step-up transformer is added has to be tuned to avoid trouble).

[I_Forgot]

Originally posted by Eva
A class D amplifier would be a good alternative for driving a highly reactive load because all the reactive energy is returned back to the PSU. In case of a capacitive load (ESL), the amplifier may be designed so that the load forms part of the output LC filter (although the resonance that results when the step-up transformer is added has to be tuned to avoid trouble).

Alternatively, you could do class D and use an HV output bridge to drive the panel directly. You'd need some high voltage switches and they'd have to be fast. I don't know if there are such devices anywhere.

I_F

[Calvin]

Hi,

Yeah, a HV-D-amp would be fine thing. But apart from the parts prob You´ll probabely get into serious trouble with those aliens in the 17 quadrant near Wega-colony who simply are not into human music
That thing would rather be a strong emv-sender

jauu
Calvin

[phase_accurate]

I agree that a purpose-built class-d would be great for driving ESLs. But I am afraid that we might not be able to do a "classic" class-d amp that is capable of doing the desired voltage swing. I once consulted someone who was developing an amp intended to drive piezo actuators up to 1000 volts. The idea of an ordinary class-d half-bridge was given up quite quickly due to the huge voltage swings involved and the subsequent high snubber losses.

He then built a topology of multiple low(er)-voltage class-d amps that add up their voltages. I don't know if he even did them in some multiphase modulation scheme which would further reduce ripple (or make lower switching frequencies and therefore lower switching losses feasible).

A mutlibit (i.e. multi voltage output stage) delta-sigma topology might be quite cool as well !

The RF transmission problem could however be minimised IMO using conventional methods.

Regards

Charles

[mzzj]

Originally posted by I_Forgot


Alternatively, you could do class D and use an HV output bridge to drive the panel directly. You'd need some high voltage switches and they'd have to be fast. I don't know if there are such devices anywhere.

I_F

Too bad that 6.5kV IGBT's are availlable only with insane current ratings. Probably too slow, too.

Stack of low current 600-1200v mosfets would be "intresting" for switching ~6kV .

[Elvee]

There is an alternative I've already proposed, based on high frequency transformers and phase modulation:
Proposition: ESLs and Class D are a perfect match

[phase_accurate]

I completely forgot about that.
It is a clever idea indeed !

Regards

Charles